cr:5.4.4a

An additional-cost ability is a play-static ability that adds one or more asset-costs and/or effect-costs to play the source card. Additional-cost abilities are typically written in the format “As an additional cost to play this [COST],” where COST is the additional cost to be paid. An additional-cost ability is optional if the COST of the ability uses the term “may” and must be declared when playing a card.[5.1.3]